This invention relates to the field of fabricating structures through progressive layers of composite tape.
Current composite tape laying equipment uses a fixed width, fixed thickness, pre-preg fabricated tape generally comprised, in part, of bundles of synthetic fibers or filaments known as "tows". The tows are bundled into a predetermined, untwisted grouping of fibers and are bonded with a material such as epoxy, which is B-staged or partially cured to a tacky state. The tape is dispensed by a tape laying head onto a mold surface, wherein successive plys of tape are utilized to build up a desired structure. After the structure is formed by the tape, the unit is thermally cured, often in a vacuum bag placed in an autoclave.
In current equipment, the tape is cut at the end of a "lay-down" pass to match the angle formed at the edge of the part. There exists a problem in being able to selectively compact the angled end portion of the tape to the part structure without also compacting the mating angled portion (tail) of the tape remaining on the dispensing reel. Further, this tail must be retracted in preparation for laying the next ply, or course, of tape. The problem of handling the tail is particularly apparent when using wide tape and cutting a steep angle, since these conditions result in a long tail being formed. On conventional state-of-the-art tape heads, the angle on the leading edge of the tape will be the complement of the angle cut on the end of the previously laid piece of tape. If this is not the required starting angle for the next lay the tape will then have to be recut before starting, or else trimmed off after laying, resulting in considerable waste of very expensive material.
Since conventional tape heads lay a constant width and constant thickness tape it is felt by the inventor that it would be an advantage to have a system where the thickness of the composite tape could be varied slightly to allow the tape to be feathered from a relatively thick section, for a highly stressed area, down to a thin section in a lightly stressed area. It is further felt that it would be desirable to have a tape laying head which can vary the width of the tape so that the tape may form openings or voids if desirable.
Conventional tape laying heads require a critical setting for the depth of cut taken by the tape cutter, since the cutter or knife must be capable of cutting through the composite tape entirely without shearing the backing paper. The backing paper is required to transport the tape and is subject to breaking if scored across its width.
Applicant has obviated the difficulties inherent in the conventional tape laying heads used in the field of composite tape structures, by means of a novel tape laminator which creates a predetermined quantity of relatively wide tape formed in situ on the machine from individually supplied relatively narrow bonded tows in the tape laying head.